Iron chromium molybdenum titanium base alloy



United States Patent 1 2,740,711 IRON CHROMIUM MOLYBDENUM TITANIUM BASE ALLOY Schuyler A. Herres and Thomas K. Redden, Albany,

N. Y., assignors to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Application April 29, 1952, Serial No. 285,078 4 Claims. (Cl. 75175.5)

This invention relates to a new and improved titanium base alloy having ternary metal alloying additions of iron, chromium and molybdenum, and wherein oxygen and nitrogen are maintained within maximum limits.

This application is a continuation-in-part of our copending application No. 118,723 of September 29, 1949 entitled Titanium Alloys.

It has been an object of our present invention to produce a relatively inexpensive titanium alloy having a stabilized all beta phase structure;

Another object is to provide an improved titanium base alloy which may make use of term alloys as additional agents in the melt;

A further object has been to produce titanium base alloys which are substantially free of intermetallic compounds and their resultant harmful effects;

These and many other objects of our invention will appear to those skilled in the art from the following description.

The alloying content of our alloy is critical and particularly, from the standpoint of a retained beta bodycentered cubic form of lattice structure which is characteristic of titanium metal when heated above about 1625 F. The alloy here being considered saves scarce and strategic elements and is suitable for structural purposes, such as in airplanes, where the service temperature does not go above about 400 F. and a good ductility is needed with a high tensile strength.

Unalloyed titanium normally exists in a hexagonal, closely-packed, crystalline structure at room temperature and transforms on heating to above about 1625 F. to a body-centered cubic lattice crystalline structure. The present invention deals with alloying additions stabilizing and completely retaining the high temperature beta structure of titanium, so that it is fully available at room temperature without the presence of alpha phase titanium. In this manner, we have been able to produce an alloy having an excellent ductility with a good tensile strength, impact, and other properties.

Reheating an alloy of the present invention within a range of about 500 to 1100 F. after its solution heat treatment will result in a decomposition of the retained beta phase, a resultant precipitation of the alpha phase, and serious loss of ductility. The alloy is, however, very useful in service at room temperature up to about 400 5 F. due to its combination of high strength and good ductility. Also, it is capable of being cold worked and annealed, thus facilitating the processing of sheet and strip products.

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In carrying out our invention, we employ a titanium base alloy of the following composition:

Table I 5 General Range Optimum Range M0=1.5 to Mo=2.5 to 6.5%

10 Cr=1.5 to 11 a Or=2.5 to 6.5% Fe=3.0 to 8 a Fe=3.5 to 6.0% 02=.20% max. 0g=.20% max. N|==.10% max. N,= 10% max In the above alloys, the remainder is titanium with incidental impurities or substantially all titanium and the alloying element contents are critical in their specified ranges. The metal alloying elements are also critical in their total content (molybdenum iron chromium) in that such total should be above about 11.00% and be low about 20%; the optimum range being about 13 to 16%.

We have found that the three metal elements in combination all tend to stabilize the beta phase of titanium. Further, the use of these metal elements within the ranges specified produces an alloy which is more stable than one made from one of the elements alone and produces an alloy that is free from the harmful effects due to the presence of intermetallic compounds that are present in binary iron-titanium and chromium-titanium alloying systems. The metal alloying elements, as an optimum, are introduced at one time to the melt and as ferro alloyadditions. The latter type of additions are more readily soluble in the melt and are less scarce and strategic than the single elements, themselves. The total content of the metal alloying elements is highly critical and particularly so from the standpoint of the retention of the beta phase of titanium.

4 Heat treatment consists of a solution treatment in the range of about 1200" to 1500" F., followed by air cooling. This treatment provides an all beta-phase structure having the required ductility and tensile properties. The alloys may be hot worked within a range of about 1200 to 1700 F. and may also be cold worked at room tem perature to produce a resultant increase of tensile strength and decrease in ductility. Titanium of commercial purity may be used in making the alloys, but it is important to maintain the oxygen and nitrogen gaseous alloying elements within the previously specified maximum amounts to obtain requisite properties.

The following is indicative of the properties of alloys of our alloy invention after they have been solution treated in the manner previously explained. Melt N0. K669 which has a total metal alloying content of 11%, illustrates the importance of the lower critical total metal alloying content. Melt K662 which has a molybdenum content that is well below the critical minimum of 1.5% required and is thus not an alloy of our invention, illustrates the importance of the individual contents of the metal alloying elements:

amount up to about .10% maximum, about 1.5 to 10% molybdenum, about 1.5 to 11% chromium, about 3 to Table 1] Composition Us F B .10 I 61 1d a1 Ingot Heat aiiii inciiig Ele mgnt u 'flg gf @53 Hard- MJ' [ha/511.111 cent cent FeOr, FeMo, Fe, Cr, Mo,

Per- Per- Per- Per- Percent cent cent cent cent K512. 10 5.7 7.0 0.3 173,000 11 10 332 0 a 3. s 0. 3 1. 9 107, 000 332 10 2 3. 75 7.0 1.25 107,000 1 1.0 311 2 10 4. 25 1.4 0.35 150. 000 19 48.7 321 4 s 4.15 2.8 5.05 158, 500 12 48 305 s 4 3. 9 5. e 2. 5 158, 500 14 47 310 :4 0 4. 2 2.1 5. 7 165, 000 12 54 345 15 3 5.0 10.5 1.0 153, 500 22 47 310 a 15 5. -15 2.1 0. 45 170, 500 21 42 311 5.5 5.5 11.05 3.55 3.5 138, 000 0 0 332 As a further example, we have chosen three alloys 8% iron, and the remainder titanium with incidental imof our invention having a total of 15% (within the optipurities; the total metal alloying content of molybdenum, mum range) of metal alloying content: chromium and iron being highly critical within the range 25 f about 11 to 207 Table III 0 2. A titanium base alloy as defined 1n cla1m 1 wherein the total metal alloying content is within a range of about Composition T fie R d f 13 m 16% 911.8 9 11C 1011 mm Strength Elmgauon of Area 3. A titanium alloy composition having an all betaor phase structure as solution treated at a temperature within a range of 1200 to 1500 R, followed by air cooling, i1; 2: 3 $13 2:3 33 2% which structure is Wholly stable at room temperature, and 3 5.25 5- 25 4-5 0 23 43 which alloy composition consists of oxygen in the amount up to about 20% maximum, nitrogen in the amount up to In the above Table III, the alloys were tested as one 35 about 11% maximum, about 2.5 to 6.5% each of molyb half inch square bars annealed 1400 F. for one half denum and chromium, about 3.5 to 6% iron, the molybhour and air cooled. denum plus chromium plus iron content being within a The result of reheating the alloys of Table III after highly critical range of above about 11% and below about a solution heat treatment is indicated as follows: 20%, and the remainder titanium with incidental impurities. Table IV 4. An improved titanium base alloy as defined in claim i 11 wherein the total molybdenum plus chromium plus F Rockwell 0" Hardness After I di t d iron content is within a range of about 13 to 16%. 1 Heat Treatment References Cited in the file of this patent Item Fe Cr Mo 1500 1%., 45 +500 +700 +700 +000 UNITED STATES PATENTS 1 min. 6 F., 6 F., 24 F., 24 1 Water hrs. hrs. hrs. hrs. 2,554,031 Ialfee 61; al May 22, 195i Quench 2,575,962 Jalfee et a1. Nov. 20, 1951 34 5 5 2,588,007 Jaifce Mar. 4, 1952 3:3 318 3530 33:3 241?, 2,640,773 Pitler June 2, 1953 5.25 4.5 30.0 44.0 48.0

FOREIGN PATENTS What we claim is: 5 718,822 Germany Mar. 24, 1942 l. A titanium base alloy composition having an all beta-phase structure as solution treated at a temperature OTHER REFERENCES of about 1200 or 1500 F., followed by air cooling, Product Engineering, November 1949. Page 150. which structure is wholly stable at room temperature, Journal of Metals, March 1950. Pages 539-552. and which alloy composition consists of oxygen in the Industrial and Engineering Chemistry, February 1950.

amount up to about 20% maximum, nitrogen in the Pages 222-226. 

1. A TITANIUM BASE ALLOY COMPOSITION HAVING AN ALL, BETA-PHASE STRUCTURE AS SOLUTION TREATED AT A TEMPERATURE OF ABOUT 120* OR 1500* F., FOLLOWED BY AIR COOLING, WHICH STRUCTURE IS WHOLLY STABLE AT ROOM TEMPERATURE, AND WHICH ALLOY COMPOSITION CONSISTS OF OXYGEN IN THE AMOUNT UP TO ABOUT .20% MAXIMUM, NITROGEN IN THE AMOUNT UP TO ABOUT .10% MAXIMUM, ABOUT 1.5 TO 10% MOLYBDENUM, ABOUT 1.5 TO 11% CHROMIUM, ABOUT 3 TO 8% IRON, AND THE REMAINDER TITANIUM WITH INCIDENTAL IMPURITIES; THE TOTAL METAL ALLOYING CONTENT OF MOLYBDENUM, CHROMIUM AND IRON BEING HIGHLY CRITICAL WITHIN THE RANGE OF ABOUT 11 TO 20%. 